Variable pulley transmissions for transferring torque from an input shaft to an output shaft have been used for some time. In such arrangements a first pulley is mounted on the input shaft, and this pulley has at least one flange axially movable relative to its other flange to change the effective pulley diameter. A second, similarly adjustable pulley is mounted on the output shaft. A flexible belt intercouples the two pulleys to transfer torque between them. As the effective diameter of one pulley is changed, and simultaneously the effective diameter of the other pulley is changed in the opposite direction, the drive ratio between the input and output shafts is adjusted in smooth, continuous manner.
For over 30 years automotive engineers have recognized that the maximum operating efficiency of the engine could be achieved if the transmission could be controlled by adjusting to different loads and speed ratios such that the engine is maintained at its maximum efficiency point. This is not possible with a conventional geared transmission in which the drive ratio is adjusted in discrete steps, rather than continuously. Accordingly, efforts have been directed to the use of a continuously variable transmission of the type described above. This has resulted in the production and marketing in Europe of the Daf passenger car, using a flexible rubber belt in such a continuously variable transmission (CVT). Such a belt is subject to wear by reason of the torque it must handle and operates under severe temperature, vibration and other adverse conditions. Accordingly, efforts have been channeled to produce a flexible belt of metal, and some of these efforts are described in the patent literature.
By way of example, U.S. Pat. No. 3,720,113, shows generally V-shaped push blocks which are described as being made of non-compressible material, such a metal. They are also shaped to tilt with respect to each other when entrained around a disc or pulley. The blocks in U.S. Pat. No. 3,949,621 are described as trapezoidal in profile and of metal. A pair of slots, each intersecting an edge, is provided to receive the endless member. The blocks of non-deformable material described in U.S. Pat. No. 4,080,841 have a "window" or opening, and the surface of the block window of the block which comes in contact with the endless band is convexly curved in the transverse direction.
All of the push blocks described in the aforesaid patents require extensive machining to provide smooth surfaces in the opening or window of the blocks which contact the endless members, in an attempt to prevent damage to the endless members as the blocks move along the endless member. However this machining is expensive and raises the cost of a CVT to a level where it may not be commercially competitive. It is thus a prime consideration of the present invention to produce a block for use with a CVT or a fixed pulley transmission which is significantly less expensive than blocks produced according to earlier teachings.